content/browser/accessibility/browser_accessibility_state_impl.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
   6 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_
   7
   8 #include <vector>
   9
  10 #include "base/basictypes.h"
  11 #include "base/compiler_specific.h"
  12 #include "base/memory/singleton.h"
  13 #include "content/common/view_message_enums.h"
  14 #include "content/public/browser/browser_accessibility_state.h"
  15
  16 namespace content {
  17
  18 // The BrowserAccessibilityState class is used to determine if Chrome should be
  19 // customized for users with assistive technology, such as screen readers. We
  20 // modify the behavior of certain user interfaces to provide a better experience
  21 // for screen reader users. The way we detect a screen reader program is
  22 // different for each platform.
  23 //
  24 // Screen Reader Detection
  25 // (1) On windows many screen reader detection mechinisms will give false
  26 // positives like relying on the SPI_GETSCREENREADER system parameter. In Chrome
  27 // we attempt to dynamically detect a MSAA client screen reader by calling
  28 // NotifiyWinEvent in NativeWidgetWin with a custom ID and wait to see if the ID
  29 // is requested by a subsequent call to WM_GETOBJECT.
  30 // (2) On mac we detect dynamically if VoiceOver is running.  We rely upon the
  31 // undocumented accessibility attribute @"AXEnhancedUserInterface" which is set
  32 // when VoiceOver is launched and unset when VoiceOver is closed.  This is an
  33 // improvement over reading defaults preference values (which has no callback
  34 // mechanism).
  35 class CONTENT_EXPORT BrowserAccessibilityStateImpl
  36     : public base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>,
  37       public BrowserAccessibilityState {
  38  public:
  39   BrowserAccessibilityStateImpl();
  40
  41   static BrowserAccessibilityStateImpl* GetInstance();
  42
  43   virtual void EnableAccessibility() OVERRIDE;
  44   virtual void DisableAccessibility() OVERRIDE;
  45   virtual void OnScreenReaderDetected() OVERRIDE;
  46   virtual bool IsAccessibleBrowser() OVERRIDE;
  47   virtual void AddHistogramCallback(base::Closure callback) OVERRIDE;
  48
  49   virtual void UpdateHistogramsForTesting() OVERRIDE;
  50
  51   AccessibilityMode accessibility_mode() const { return accessibility_mode_; };
  52   void SetAccessibilityMode(AccessibilityMode mode);
  53
  54  private:
  55   friend class base::RefCountedThreadSafe<BrowserAccessibilityStateImpl>;
  56   friend struct DefaultSingletonTraits<BrowserAccessibilityStateImpl>;
  57
  58   // Called a short while after startup to allow time for the accessibility
  59   // state to be determined. Updates histograms with the current state.
  60   void UpdateHistograms();
  61
  62   // Leaky singleton, destructor generally won't be called.
  63   virtual ~BrowserAccessibilityStateImpl();
  64
  65   void UpdatePlatformSpecificHistograms();
  66
  67   AccessibilityMode accessibility_mode_;
  68
  69   std::vector<base::Closure> histogram_callbacks_;
  70
  71   DISALLOW_COPY_AND_ASSIGN(BrowserAccessibilityStateImpl);
  72 };
  73
  74 }  // namespace content
  75
  76 #endif  // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_STATE_IMPL_H_